10 68 Proceedings of the Royal Irish Academy. 



merely as a parachute-apparatus on the ripe fruit are in my view to be con- 

 sidered as a transpiration-apparatus for the ripe fruit, and these subsequently 

 can be used for distribution, but are not necessarily for this." 1 Guppy, as 

 already mentioned (p. 60), is inclined to treat dispersal-mechanisms as 

 by-products, so to speak, in the plant's life-history. The reader dipping into 

 the subject of the pappus may also consult the papers of Taliew, 2 Hirsch, 3 and 

 Steinbrinck. 1 



The pappus reaches its most beautiful development in some of the 

 Cynaroeephaleae, such as the common Spear Thistle. Here the comparatively 

 large and heavy seed is surmounted by a beautiful shuttlecock of stiff spines, 

 eight times the length of the seed, each spine clothed with short branches, which 

 greatly increase its efficacy ; while the seed alone falls 12 feet in less than one 

 second, the presence of the pappus reduces this velocity to about -rrth (12 feet 

 in 14 seconds). The pappus alone takes 28 seconds to fall the same distance. 

 An attempt to calculate the efficacy of the pappus and deduce the velocity of 

 fall in the allied C. arvensis is made by Dandeno 5 ; but his result is only about 

 half the observed rate. The lightness of these parachute-seeds is shown by 

 Bessey's calculation that a Dandelion seed weighs "00044 gramme, or about 

 one-millionth of a pound. 6 



In the case of this and many other Composites, the hairs of the pappus are 

 stiff and elastic ; but in the Sow-thistles (Sonchus), as well as in very 

 efficient flying seeds of other orders (e.g., Epilobium), the hairs are lax, and 

 cling easily to any surface except a very smooth one — thus supplying a second 

 means of dispersal, such as is possessed by seeds furnished with hooks or 

 barbs. Prieb 7 believes that animal-dispersal is effective in the case of many 

 pappus -bearing species ; and Kronfeld' points out that in some eases, e.g., 

 Taraxacum — the pappus assists water-dispersal by keeping the achene afloat. 



But in the Compositae we are again faced by the fact that apparently 

 distribution bears no proportion to ease of dispersal "We may arrange a 



1 Goebel : Organography of Plants (Englished.), ii., pp. 570, 571. 1905. 



2 W. Tailew : Ueber das hydroskopische Gewebe der Compositen- Pappus. Kazan, 1894 (in 

 Russian). Abstract in Bot. Centralblatt, lxiii., pp. 320-324. 1895. 



3 Arnold Hlrsch : TTeber den Bewcgungsmechanismns der Kompositenpappus. 1901. Abstract 

 in Bot. Centralblatt, Ittt it, p. 248. 



4 C. Stei>bui>ck: Zum Bewegungsmechanismus der Kompositenpappus. Berichte Deutsch. Bot. 

 Gesellschaft, xix., pp. 514-515. 1901. 



5 J. B. Da>de>.-o: Tie Parachute Effect of Thistle-down. Science pf.T.), >-.s., xxii., 

 pp. 568-572. 1905. 



6 C. E. Bessey : Weight oi Dandelion-down. Science (N.T.), N.S., xx., p. 119. 1904. 



7 B. Fkieb : Der Pappus als YerDreitungsmittel aer Compositenfruchte. Oest. Bot. Zeitschrift, 

 Wien, li., pp. 92-96. 1901. 



5 iloriz Kboxfeld : Uber einige Terbreitungamittel der Compositenfruchte. Sitz. k. Akad. der 

 Wissensch., Wien, Math. ->"at. Klasse, xci., Abth. i, pp. 414-428. 1885. 



